Recently several patents issued disclosing new types of polyurethane hydrogel polymers and methods for their production; namely, U.S. Pat. No. 3,939,105, U.S. Pat. No. 3,939,123 and U.S. Pat. No. 3,940,542. In these patents the hydrogels are produced by methods involving the use of solvents. As a consequence additional costs are incurred and, also, steps to recover the solvents to avoid environmental pollution are required, which add to the cost of the product. The present invention relates to an improved process that eliminates the use of the solvents and can, if desired, produce the hydrogel polymers in the shaped form desired, such as film, fiber, rod, pellet, etc. As is known, hydrogels, due to their absorbency characteristics, have found many uses, usually in conjunction with other materials.
The use of fibrous materials as absorbents for moisture is a well known, widespread practice. In this application many of the natural and synthetic fibers have been used and extensive efforts have been made to improve their absorption properties. One of the major deficiencies of the natural and synthetic materials heretofore used has been their tendency to release the absorbed moisture when pressure has been applied to the moisture containing material. The fact that pressure causes the absorbed fluid to be expelled from the fibers is known as reversible absorption. For many applications, however, irreversible absorption is desired, for example, in surgical dressings, diapers, bed pads, catamenials, and the like, whereby the absorbed moisture is retained in the absorbent material under an applied pressure.
Within the past decade innovations have resulted in the production of hydrogels, which have such irreversible absorption properties, in powder or particulate form and even, in some instances, in film form using processes which require the use of solvents. An especially interesting characteristic of the hydrogel polymers is that when in contact with water they absorb it and swell to a certain point and then stop further absorption; however, the final swollen polymer is still similar in shape to its initial unswollen shape. Thus, many of the hydrogels have the ability to absorb many times their original weight in water without becoming soggy or deformed. In general, the hydrogels are used in conjunction with other materials as supports. Among other U.S. patents that have issued in this field are U.S. Pat. No. 3,669,103; U.S. Pat. No. 3,589,364; U.S. Pat. No. 3,694,301; U.S. Pat. No. 3,670,731; U.S. Pat. No. 3,164,565. This is but an exemplary listing and should not be considered complete.